Optimising biogas production through co-digestion of sewage sludge with food waste and FOG

This study focused on the assessment of co-digestion of sewage sludge (SS), food waste (FW) and fat, oil and grease (FOG) to optimise biogas production. A series of batch experiments were conducted under mesophilic conditions with different mixtures of SS, FW, and FOG to optimise the best mixing ratio. The performance of the reactors was assessed based on cumulative methane potential, volatile fatty acid (VFA) effects, ammonium (NH4+-N) effects, soluble chemical oxygen demand (SCOD), volatile solids (VS) and, total solids (TS) removal efficiency. The cumulative methane production of mono-digestion of SS, FW, and FOG is 346, 428 and 898 NmL CH4/g VS added, respectively, while the mixture of SS, FW, and FOG with a ratio of 70:25:5 (w/w) could achieve the best methane production of 771 NmL CH4/g VSadded. There was moderate inhibition of VFAs, which could be overcome with a reduction in organic loading rate (OLR) and FW adjustment. NH4+-N was not an inhibition factor in this study. The result also shows a linear increase in methane production and VS reduction in the digestion of the co-mixture of the substrates. Co-digestion can contribute to renewable energy production, diversion of organic waste from landfill and reduction of greenhouse gas (GHG) emissions. Economic and environmental benefits of co-digestion adoption by Ireland wastewater treatment plants (WWTPs) were extensively analyzed and discussed